We’re often asked what a talkgroup is, and what all the rest of the jargon is all about, after all, you’re on the right frequency – you should hear stuff right ? – Wrong !

In FM simplex it’s easy to exchange audio, you just TX and you will hear the audio coming out of your receiver, it’s very simple, but we can and do use CTCSS too, this is really handy, as you don’t get the FM squelch ‘chuffing’ or suddenly opening and disturbing you when you have the squelch set finely or local noise unmutes the receiver.

Most of us will undoubtedly remember the 1750hz toneburst used to access repeaters, which some older amateur repeaters still use, which was needed back then, as carrier-access repeaters were generally regarded as a bad thing.. imagine an interfering noise source local to the repeater on it’s input frequency, holding the repeater open.. staying open for hours on end, just relaying noise, and all that entails, thank goodness for CTCSS too.

CTCSS also added the ability to have multiple groups of users all on the same frequency, all using different CTCSS tones, and all with Groups of users being able to hear only each other in the same group , while other groups using different CTCSS tones on the same frequency, only heard their users.. and so on, this of course, also works on repeaters, used to most noticeably on the ‘community repeater’.

In DMR, the three most confusing terms that new users come across are Talkgroups, slots, (or timeslots), and colour codes. the word ‘Talkgroup‘ comes from the crazy world of trunking or Trunked radio systems, where we in the UK are most familiar with MPT type trunking channels as the constantly transmitting ‘control channel’ often heard in the commercial PMR segments of the VHF and UHF bands

As for colour codes – i would say just think of them as a DMR version of CTCSS. and Timeslots – well in simple terms, DMR has two to choose from, each is it’s own seperate RF channel, and mostly slots only matters when using a DMR repeater. They can be used to good effect on simplex too, but for now, slots can be thought of as just a ‘repeater slot’ TETRA has 4 timeslots, and some French system, which was called Detranet i think, has three – but importantly they’re all TDMA (more of which, in another article coming later)

So, lets consider setting up a rig’s codeplug so that we can access our local DMR repeater, we know the frequency, we know the colour code and all we need to know now, is the talkgroup ID It’s a number, which we give a descriptive name to like ‘UK Wide‘ or ‘Local TG9‘ or whatever, it doesn’t really matter exactly *what* they’re named in your radio, as long as the Talkgroup ID Number is correct, and what you’ve named it UK Wide or something similar which makes sense, like on the DMR-MARC talkgroups.

Talkgroups are just ‘virtual channels’ and you can have many different Talkgroups on a single frequency, and like CTCSS – each different talkgroup only hears calls from the same talkgroup number (ID) programmed in the transmitter. you can not transmit on talkgroup 9 and pick it up on a rig programmed only to receive talkgroup 1.On the DMR-MARC network there are many Talkgroups in use around the world, and there is a list of used Talkgroups HERE – no DMR-MARC repeater carries them *all* and most here in the UK use about a half dozen talkgroups, or variations thereof.
Below is a condensed list of Talkgroups commonly used on most UK DMR-MARC repeaters

Talkgroup ID number 1: slot 1:Worldwide, all-language callingTalkgroup, used only if you are calling worldwide, QSY to up to the most local Talkgroup you can. QSO’s on here, if allowed, must be short.

Talkgroup ID number 2: slot 1:European-wide multi-language Talkgroup, also on , this Talkgroup can be used for QSOs presently, as always, it is recommended to change to a more local Talkgroup whenever possible.

Talkgroup ID number 8: slot 2:Roaming, used for roaming between neighbouring repeaters, Your rig, if correctly configured, will automatically switch to the next strongest repeater as it comes into range whilst you are mobile – something like a mobile phone does when physically moving between ‘cells’ of differing strengths

Talkgroup ID number 9: slot 2Local calls, This is used for QSO’s between users on the same local repeater, this talkgroup is not routed across to other repeaters, and is more like a standard repeater.

(NBTG 9 is most used for simplex DMR in the UK also, but you can use any, and any colour code)

Talkgroup ID number 13: slot 1Worldwide, This is for International English language QSOs only.

Talkgroup ID number 235: slot 1 (was slot 2)UK only, calls on this Talkgroup are for QSOs between UK Amateurs Nationwide, where TG8, TG9 or simplex would not work.

Every repeater can carry their own mix of talkgroups as per the repeater groups wishes or requirements, so do not necessarily expect these talkgroups to always be available all of the time, the network is growing and adjustments are being made accordingly to accommodate more users, provide more facilities, solving issues and to be more efficient.
There is much more to DMR of course than this basic introduction, and there is more to talkgroups too, like the All-Calls Talkgroup and private calling, to name just a couple, but I’ll leave you to discover those for now…

Hi, Its not a rule as such, but it does makes some sense to put all of the ‘non-UK’ traffic on to slot 1 (for example) thereby leaving the other slot free for more local traffic.
Using other non-UK talkgroups on, (in this case) slot 2 also would render the local repeater unusable to its local users if international calls were being relayed on both slots at the same time.

Well Thank Chaps, hopefully my adventure off into CTCSS land didn’t distract too much from the point i was trying to make about introducing the user to the idea of ‘groups’. Heck, some of it might even be right .. any additions or errors – please let us know – then we can share these concepts discussed to help demystify the mode.

Hi there would it be possible to take some extracts from your really useful document “Talkgroups – and pick a colour, any colour ..” and add it to the users guide appendix I am producing for the UK-DMR, thanks in aticipation, dave

Well that has helped me to some level of understanding how the DMR frequency/slot/time slot/channel/talkgroup/colour code works but I would still like to see it in a block diagram or roadmap style layout as that would set it in stone for me, I will soon be receiving my MD380 and realy want to understand all this. Saying all that this has been the best yet.

Glad it was of some help Phil … time restraints at the moment dont allow me at present to make any more graphics or anything too fancy at present, the next graphic i would like to construct is a graphical animated GIF depicting what TDMA is, and why it’s got it’s own secret sauce as compared to FDMA.